Conventionally, in a production line mixedly including robot operation steps and manual operation steps such as an automobile body assembly line, in the case where trouble such as malfunction occurs in a robot during an assembly operation in the robot operation step, the malfunction of the robot is detected by a detection device, a transfer device in the production line is urgently stopped while a warning based on the detection is issued, the assembly operation by the robot is stopped, and the robot is returned to its original position.
Then, after a maintenance operator confirms that there is no problem in safety and production in the robot operation step, a backup operator is located in a backup step downstream of the robot operation step where the trouble occurs. Then, the transfer device is operated again, the backup operator performs an uncompleted operation of the robot in the backup step, and the maintenance operator performs a repair operation of the robot in the robot operation step (for example, see Patent Documents 1 to 3).    Patent Document 1: Japanese Patent Application Publication No. 63-284075    Patent Document 2: Japanese Patent Application Publication No. 5-105138    Patent Document 3: Japanese Patent Application Publication No. 6-190662